xen-netback: add control ring boilerplate

My recent patch to include/xen/interface/io/netif.h defines a new shared
ring (in addition to the rx and tx rings) for passing control messages
from a VM frontend driver to a backend driver.

This patch adds the necessary code to xen-netback to map this new shared
ring, should it be created by a frontend, but does not add implementations
for any of the defined protocol messages. These are added in a subsequent
patch for clarity.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 277 insertions, 30 deletions

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index f44b38846420..093a12abf71f 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -260,6 +260,11 @@ struct xenvif {
         struct dentry *xenvif_dbg_root;
 #endif
 
+        struct xen_netif_ctrl_back_ring ctrl;
+        struct task_struct *ctrl_task;
+        wait_queue_head_t ctrl_wq;
+        unsigned int ctrl_irq;
+
         /* Miscellaneous private stuff. */
         struct net_device *dev;
 };
@@ -285,10 +290,15 @@ struct xenvif *xenvif_alloc(struct device *parent,
 int xenvif_init_queue(struct xenvif_queue *queue);
 void xenvif_deinit_queue(struct xenvif_queue *queue);
 
-int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
-                   unsigned long rx_ring_ref, unsigned int tx_evtchn,
-                   unsigned int rx_evtchn);
-void xenvif_disconnect(struct xenvif *vif);
+int xenvif_connect_data(struct xenvif_queue *queue,
+                        unsigned long tx_ring_ref,
+                        unsigned long rx_ring_ref,
+                        unsigned int tx_evtchn,
+                        unsigned int rx_evtchn);
+void xenvif_disconnect_data(struct xenvif *vif);
+int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
+                        unsigned int evtchn);
+void xenvif_disconnect_ctrl(struct xenvif *vif);
 void xenvif_free(struct xenvif *vif);
 
 int xenvif_xenbus_init(void);
@@ -300,10 +310,10 @@ int xenvif_queue_stopped(struct xenvif_queue *queue);
 void xenvif_wake_queue(struct xenvif_queue *queue);
 
 /* (Un)Map communication rings. */
-void xenvif_unmap_frontend_rings(struct xenvif_queue *queue);
-int xenvif_map_frontend_rings(struct xenvif_queue *queue,
-                              grant_ref_t tx_ring_ref,
-                              grant_ref_t rx_ring_ref);
+void xenvif_unmap_frontend_data_rings(struct xenvif_queue *queue);
+int xenvif_map_frontend_data_rings(struct xenvif_queue *queue,
+                                   grant_ref_t tx_ring_ref,
+                                   grant_ref_t rx_ring_ref);
 
 /* Check for SKBs from frontend and schedule backend processing */
 void xenvif_napi_schedule_or_enable_events(struct xenvif_queue *queue);
@@ -318,6 +328,8 @@ void xenvif_kick_thread(struct xenvif_queue *queue);
 
 int xenvif_dealloc_kthread(void *data);
 
+int xenvif_ctrl_kthread(void *data);
+
 void xenvif_rx_queue_tail(struct xenvif_queue *queue, struct sk_buff *skb);
 
 void xenvif_carrier_on(struct xenvif *vif);
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index f5231a2dd2ac..78a10d2af101 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -128,6 +128,15 @@ irqreturn_t xenvif_interrupt(int irq, void *dev_id)
         return IRQ_HANDLED;
 }
 
+irqreturn_t xenvif_ctrl_interrupt(int irq, void *dev_id)
+{
+        struct xenvif *vif = dev_id;
+
+        wake_up(&vif->ctrl_wq);
+
+        return IRQ_HANDLED;
+}
+
 int xenvif_queue_stopped(struct xenvif_queue *queue)
 {
         struct net_device *dev = queue->vif->dev;
@@ -527,9 +536,66 @@ void xenvif_carrier_on(struct xenvif *vif)
         rtnl_unlock();
 }
 
-int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
-                   unsigned long rx_ring_ref, unsigned int tx_evtchn,
-                   unsigned int rx_evtchn)
+int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
+                        unsigned int evtchn)
+{
+        struct net_device *dev = vif->dev;
+        void *addr;
+        struct xen_netif_ctrl_sring *shared;
+        struct task_struct *task;
+        int err = -ENOMEM;
+
+        err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
+                                     &ring_ref, 1, &addr);
+        if (err)
+                goto err;
+
+        shared = (struct xen_netif_ctrl_sring *)addr;
+        BACK_RING_INIT(&vif->ctrl, shared, XEN_PAGE_SIZE);
+
+        init_waitqueue_head(&vif->ctrl_wq);
+
+        err = bind_interdomain_evtchn_to_irqhandler(vif->domid, evtchn,
+                                                    xenvif_ctrl_interrupt,
+                                                    0, dev->name, vif);
+        if (err < 0)
+                goto err_unmap;
+
+        vif->ctrl_irq = err;
+
+        task = kthread_create(xenvif_ctrl_kthread, (void *)vif,
+                              "%s-control", dev->name);
+        if (IS_ERR(task)) {
+                pr_warn("Could not allocate kthread for %s\n", dev->name);
+                err = PTR_ERR(task);
+                goto err_deinit;
+        }
+
+        get_task_struct(task);
+        vif->ctrl_task = task;
+
+        wake_up_process(vif->ctrl_task);
+
+        return 0;
+
+err_deinit:
+        unbind_from_irqhandler(vif->ctrl_irq, vif);
+        vif->ctrl_irq = 0;
+
+err_unmap:
+        xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
+                                vif->ctrl.sring);
+        vif->ctrl.sring = NULL;
+
+err:
+        return err;
+}
+
+int xenvif_connect_data(struct xenvif_queue *queue,
+                        unsigned long tx_ring_ref,
+                        unsigned long rx_ring_ref,
+                        unsigned int tx_evtchn,
+                        unsigned int rx_evtchn)
 {
         struct task_struct *task;
         int err = -ENOMEM;
@@ -538,7 +604,8 @@ int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
         BUG_ON(queue->task);
         BUG_ON(queue->dealloc_task);
 
-        err = xenvif_map_frontend_rings(queue, tx_ring_ref, rx_ring_ref);
+        err = xenvif_map_frontend_data_rings(queue, tx_ring_ref,
+                                             rx_ring_ref);
         if (err < 0)
                 goto err;
 
@@ -614,7 +681,7 @@ err_tx_unbind:
         unbind_from_irqhandler(queue->tx_irq, queue);
         queue->tx_irq = 0;
 err_unmap:
-        xenvif_unmap_frontend_rings(queue);
+        xenvif_unmap_frontend_data_rings(queue);
         netif_napi_del(&queue->napi);
 err:
         module_put(THIS_MODULE);
@@ -634,7 +701,7 @@ void xenvif_carrier_off(struct xenvif *vif)
         rtnl_unlock();
 }
 
-void xenvif_disconnect(struct xenvif *vif)
+void xenvif_disconnect_data(struct xenvif *vif)
 {
         struct xenvif_queue *queue = NULL;
         unsigned int num_queues = vif->num_queues;
@@ -668,12 +735,32 @@ void xenvif_disconnect(struct xenvif *vif)
                         queue->tx_irq = 0;
                 }
 
-                xenvif_unmap_frontend_rings(queue);
+                xenvif_unmap_frontend_data_rings(queue);
         }
 
         xenvif_mcast_addr_list_free(vif);
 }
 
+void xenvif_disconnect_ctrl(struct xenvif *vif)
+{
+        if (vif->ctrl_task) {
+                kthread_stop(vif->ctrl_task);
+                put_task_struct(vif->ctrl_task);
+                vif->ctrl_task = NULL;
+        }
+
+        if (vif->ctrl_irq) {
+                unbind_from_irqhandler(vif->ctrl_irq, vif);
+                vif->ctrl_irq = 0;
+        }
+
+        if (vif->ctrl.sring) {
+                xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
+                                        vif->ctrl.sring);
+                vif->ctrl.sring = NULL;
+        }
+}
+
 /* Reverse the relevant parts of xenvif_init_queue().
  * Used for queue teardown from xenvif_free(), and on the
  * error handling paths in xenbus.c:connect().
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 4412a57ec862..ff22b6daa077 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1926,7 +1926,7 @@ static inline bool tx_dealloc_work_todo(struct xenvif_queue *queue)
         return queue->dealloc_cons != queue->dealloc_prod;
 }
 
-void xenvif_unmap_frontend_rings(struct xenvif_queue *queue)
+void xenvif_unmap_frontend_data_rings(struct xenvif_queue *queue)
 {
         if (queue->tx.sring)
                 xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(queue->vif),
@@ -1936,9 +1936,9 @@ void xenvif_unmap_frontend_rings(struct xenvif_queue *queue)
                                         queue->rx.sring);
 }
 
-int xenvif_map_frontend_rings(struct xenvif_queue *queue,
-                              grant_ref_t tx_ring_ref,
-                              grant_ref_t rx_ring_ref)
+int xenvif_map_frontend_data_rings(struct xenvif_queue *queue,
+                                   grant_ref_t tx_ring_ref,
+                                   grant_ref_t rx_ring_ref)
 {
         void *addr;
         struct xen_netif_tx_sring *txs;
@@ -1965,7 +1965,7 @@ int xenvif_map_frontend_rings(struct xenvif_queue *queue,
         return 0;
 
 err:
-        xenvif_unmap_frontend_rings(queue);
+        xenvif_unmap_frontend_data_rings(queue);
         return err;
 }
 
@@ -2164,6 +2164,95 @@ int xenvif_dealloc_kthread(void *data)
         return 0;
 }
 
+static void make_ctrl_response(struct xenvif *vif,
+                               const struct xen_netif_ctrl_request *req,
+                               u32 status, u32 data)
+{
+        RING_IDX idx = vif->ctrl.rsp_prod_pvt;
+        struct xen_netif_ctrl_response rsp = {
+                .id = req->id,
+                .type = req->type,
+                .status = status,
+                .data = data,
+        };
+
+        *RING_GET_RESPONSE(&vif->ctrl, idx) = rsp;
+        vif->ctrl.rsp_prod_pvt = ++idx;
+}
+
+static void push_ctrl_response(struct xenvif *vif)
+{
+        int notify;
+
+        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->ctrl, notify);
+        if (notify)
+                notify_remote_via_irq(vif->ctrl_irq);
+}
+
+static void process_ctrl_request(struct xenvif *vif,
+                                 const struct xen_netif_ctrl_request *req)
+{
+        make_ctrl_response(vif, req, XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED,
+                           0);
+        push_ctrl_response(vif);
+}
+
+static void xenvif_ctrl_action(struct xenvif *vif)
+{
+        for (;;) {
+                RING_IDX req_prod, req_cons;
+
+                req_prod = vif->ctrl.sring->req_prod;
+                req_cons = vif->ctrl.req_cons;
+
+                /* Make sure we can see requests before we process them. */
+                rmb();
+
+                if (req_cons == req_prod)
+                        break;
+
+                while (req_cons != req_prod) {
+                        struct xen_netif_ctrl_request req;
+
+                        RING_COPY_REQUEST(&vif->ctrl, req_cons, &req);
+                        req_cons++;
+
+                        process_ctrl_request(vif, &req);
+                }
+
+                vif->ctrl.req_cons = req_cons;
+                vif->ctrl.sring->req_event = req_cons + 1;
+        }
+}
+
+static bool xenvif_ctrl_work_todo(struct xenvif *vif)
+{
+        if (likely(RING_HAS_UNCONSUMED_REQUESTS(&vif->ctrl)))
+                return 1;
+
+        return 0;
+}
+
+int xenvif_ctrl_kthread(void *data)
+{
+        struct xenvif *vif = data;
+
+        for (;;) {
+                wait_event_interruptible(vif->ctrl_wq,
+                                         xenvif_ctrl_work_todo(vif) ||
+                                         kthread_should_stop());
+                if (kthread_should_stop())
+                        break;
+
+                while (xenvif_ctrl_work_todo(vif))
+                        xenvif_ctrl_action(vif);
+
+                cond_resched();
+        }
+
+        return 0;
+}
+
 static int __init netback_init(void)
 {
         int rc = 0;
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index bd182cd55dda..6a31f2610c23 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -38,7 +38,8 @@ struct backend_info {
         const char *hotplug_script;
 };
 
-static int connect_rings(struct backend_info *be, struct xenvif_queue *queue);
+static int connect_data_rings(struct backend_info *be,
+                              struct xenvif_queue *queue);
 static void connect(struct backend_info *be);
 static int read_xenbus_vif_flags(struct backend_info *be);
 static int backend_create_xenvif(struct backend_info *be);
@@ -367,6 +368,12 @@ static int netback_probe(struct xenbus_device *dev,
         if (err)
                 pr_debug("Error writing multi-queue-max-queues\n");
 
+        err = xenbus_printf(XBT_NIL, dev->nodename,
+                            "feature-ctrl-ring",
+                            "%u", true);
+        if (err)
+                pr_debug("Error writing feature-ctrl-ring\n");
+
         script = xenbus_read(XBT_NIL, dev->nodename, "script", NULL);
         if (IS_ERR(script)) {
                 err = PTR_ERR(script);
@@ -457,7 +464,8 @@ static void backend_disconnect(struct backend_info *be)
 #ifdef CONFIG_DEBUG_FS
                 xenvif_debugfs_delif(be->vif);
 #endif /* CONFIG_DEBUG_FS */
-                xenvif_disconnect(be->vif);
+                xenvif_disconnect_data(be->vif);
+                xenvif_disconnect_ctrl(be->vif);
         }
 }
 
@@ -825,6 +833,48 @@ static void hotplug_status_changed(struct xenbus_watch *watch,
         kfree(str);
 }
 
+static int connect_ctrl_ring(struct backend_info *be)
+{
+        struct xenbus_device *dev = be->dev;
+        struct xenvif *vif = be->vif;
+        unsigned int val;
+        grant_ref_t ring_ref;
+        unsigned int evtchn;
+        int err;
+
+        err = xenbus_gather(XBT_NIL, dev->otherend,
+                            "ctrl-ring-ref", "%u", &val, NULL);
+        if (err)
+                goto done; /* The frontend does not have a control ring */
+
+        ring_ref = val;
+
+        err = xenbus_gather(XBT_NIL, dev->otherend,
+                            "event-channel-ctrl", "%u", &val, NULL);
+        if (err) {
+                xenbus_dev_fatal(dev, err,
+                                 "reading %s/event-channel-ctrl",
+                                 dev->otherend);
+                goto fail;
+        }
+
+        evtchn = val;
+
+        err = xenvif_connect_ctrl(vif, ring_ref, evtchn);
+        if (err) {
+                xenbus_dev_fatal(dev, err,
+                                 "mapping shared-frame %u port %u",
+                                 ring_ref, evtchn);
+                goto fail;
+        }
+
+done:
+        return 0;
+
+fail:
+        return err;
+}
+
 static void connect(struct backend_info *be)
 {
         int err;
@@ -861,6 +911,12 @@ static void connect(struct backend_info *be)
         xen_register_watchers(dev, be->vif);
         read_xenbus_vif_flags(be);
 
+        err = connect_ctrl_ring(be);
+        if (err) {
+                xenbus_dev_fatal(dev, err, "connecting control ring");
+                return;
+        }
+
         /* Use the number of queues requested by the frontend */
         be->vif->queues = vzalloc(requested_num_queues *
                                   sizeof(struct xenvif_queue));
@@ -896,11 +952,12 @@ static void connect(struct backend_info *be)
                 queue->remaining_credit = credit_bytes;
                 queue->credit_usec = credit_usec;
 
-                err = connect_rings(be, queue);
+                err = connect_data_rings(be, queue);
                 if (err) {
-                        /* connect_rings() cleans up after itself on failure,
-                         * but we need to clean up after xenvif_init_queue() here,
-                         * and also clean up any previously initialised queues.
+                        /* connect_data_rings() cleans up after itself on
+                         * failure, but we need to clean up after
+                         * xenvif_init_queue() here, and also clean up any
+                         * previously initialised queues.
                          */
                         xenvif_deinit_queue(queue);
                         be->vif->num_queues = queue_index;
@@ -935,15 +992,17 @@ static void connect(struct backend_info *be)
 
 err:
         if (be->vif->num_queues > 0)
-                xenvif_disconnect(be->vif); /* Clean up existing queues */
+                xenvif_disconnect_data(be->vif); /* Clean up existing queues */
         vfree(be->vif->queues);
         be->vif->queues = NULL;
         be->vif->num_queues = 0;
+        xenvif_disconnect_ctrl(be->vif);
         return;
 }
 
 
-static int connect_rings(struct backend_info *be, struct xenvif_queue *queue)
+static int connect_data_rings(struct backend_info *be,
+                              struct xenvif_queue *queue)
 {
         struct xenbus_device *dev = be->dev;
         unsigned int num_queues = queue->vif->num_queues;
@@ -1007,8 +1066,8 @@ static int connect_rings(struct backend_info *be, struct xenvif_queue *queue)
         }
 
         /* Map the shared frame, irq etc. */
-        err = xenvif_connect(queue, tx_ring_ref, rx_ring_ref,
-                             tx_evtchn, rx_evtchn);
+        err = xenvif_connect_data(queue, tx_ring_ref, rx_ring_ref,
+                                  tx_evtchn, rx_evtchn);
         if (err) {
                 xenbus_dev_fatal(dev, err,
                                  "mapping shared-frames %lu/%lu port tx %u rx %u",